As the four-day siege drew to a close last night, a witness said an AK-47-wielding ‘pale-skinned woman’ with long dark hair – the same as British Muslim convert Lewthwaite – locked eyes with her as she cowered beneath a box before opening fire from a balcony.

Amazingly, the woman, who gave her name only as Caroline, escaped unharmed as Islamists stormed the Westgate shopping centre.

She said: ‘She was high up but not far from me, close enough that I saw her looking along the floor where I was until she saw me.

‘She stopped and aimed at me and then opened fire. All of the bullets did not hit me, I don’t know how that happened.

‘She stopped firing at me for a moment and looked away and I jumped up and ran around a corner and that’s how I escaped.

‘She had pale skin and long black hair, and was wearing a baggy black top. I can’t remember very much, but I remember she had pale skin.’

A senior Kenyan anti-terror officer last night revealed that police had received many witness accounts of a female attacker resembling the widow of 7/7 bomber Jermaine Lindsay.

He added: ‘We believe that she was involved in the attack. We cannot doubt the eyewitnesses who say they saw her commanding the attackers.’

Enthusiast: Now schoolmates from Buckinghamshire have said Lewthwaite was involved with Islam in her schooldays

The vivid description of a female jihadist comes as Kenya president Uhuru Kenyatta last night confirmed he had received intelligence reports suggesting a British woman was involved.

Kenya foreign minister Amina Mohamed added: ‘The Briton was a woman... who has done this many times before.’

Yesterday, a Twitter account purporting to belong to militant group Al Shabaab also claimed that Lewthwaite had ‘commanded’ the attack.

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A post said: ‘We have received permission to disclose the involvement of Samantha Lewthwaite aka sherafiyah [her Islamic name], she successfully overseered [sic] the mission.’

British security officials say they have yet to receive confirmation from the Kenyan authorities of Lewthwaite’s role in the attack, but they would not be ‘entirely surprised’ if she is involved.

It emerged yesterday that Lewthwaite’s grandmother, 85-year-old Ellen Allen, was rushed to hospital in Banbridge, Northern Ireland after collapsing from the stress of her granddaughter’s notoriety.

In court: Lewthwaite has been on the run since police foiled her bomb plot in Mombasa, Kenya, in 2011. Yesterday, the trial for her British accomplice in this plot, Jermaine Grant (pictured), began in Mombasa

Lewthwaite, from Aylesbury, Buckinghamshire, has been on the run since police foiled her bomb plot targeting Western hotels and a shopping mall in the Kenyan coastal resort of Mombasa in December 2011.

'She stopped and aimed at me and then opened fire. All of the bullets did not hit me, I don’t know how that happened'

Witness 'Caroline'

Yesterday, the trial for her British accomplice in this plot, Jermaine Grant, began in Mombasa.

Scotland Yard anti-terror officers gave evidence for the first time, describing the chemicals found at their make-shift bomb factory.

As mother-of-four Lewthwaite’s relatives in the UK maintained a wall of silence, a former police detective told the Mail he was ‘not surprised’ to learn of her suspected role in the attack.

Noel Hogan, who interviewed the former grammar school pupil shortly before the July 7 bombings, said: ‘If Samantha is involved, it does not surprise me.’

Mr Hogan was hired by a bank to investigate why their customer, Lewthwaite’s husband Lindsay, had spent £900 on dozens of bottles of perfume over a matter of days.

Operation: Kenyan soldiers move in formation, clearing the top floor balcony and interior of the Nairobi mall

The suspicious purchases were made just days before the July 7 bombings and were used to make the homemade explosives.

'She was an average, British, young, ordinary girl. She didn’t have very good confidence'

Councillor Raj Khan on Lewthwaite

As part of his agency’s investigation, they spoke to Lewthwaite four times. Mr Hogan said: ‘On each occasion it was noted that her stories were inconsistent and her demeanour was unusual.

‘We didn’t consider her a particularly honest individual.’

Yet those who knew Lewthwaite from her hometown of Aylesbury expressed surprise at her role as one of Al Shabaab’s key financiers and bomb-making tutors.

Councillor Raj Khan said: ‘She was an average, British, young, ordinary girl. She didn’t have very good confidence. There was nothing that made me worried about her.’